1. Field of the Invention
The present invention relates to a method of manufacturing alkylphenyl alkyl ethers or thioethers by reacting alkyl phenols or thiophenols with a dialkyl or arylalkyl carbonate, in the presence of amidine catalysts.
2. Discussion of the Background
Alkylphenyl alkyl ethers as considered herein comprise the oxygen ethers and the sulfur-derivative thioethers as well.
The phenyl ethers have the following formula: ##STR2## where U represents O or S; and R.sub.1 -R.sub.6 each independently represent an alkyl or aryl group, but R.sub.1 -R.sub.5 may each independently represent a functional group other than these, including, e.g., but not limited to, --COOR, --NO.sub.2, --NH.sub.2, --O--CH.sub.2 --CH.sub.2 --OH, --OH, --CHO, or -halogen; further
R.sub.1 -R.sub.5 may be bridged by suitable bifunctional substituents, such as, e.g., --(CH.sub.2).sub.x --, or --(CH.sub.2).sub.x --Z--(CH.sub.2).sub.y -- (where Z represents a hetero atom; x=0-7, and y=0-7), or preferably unsaturated substituents such as are characteristic of anellated ring systems, e.g. (but not limited to) naphthyl, phenanthryl, anthracenyl, quinolyl, isoquinolyl, or indolyl. PA1 are toxic (e.g., phosphines and crown ether(s)); PA1 are water pollutants (e.g., tertiary amines, quaternary ammonium salts, and guanidines); PA1 are expensive (e.g., crown ethers and guanidines); PA1 can be used only once (e.g., guanidines); PA1 afford low yields per unit volume per unit time (e.g., tertiary amines); PA1 in some cases can only promote the reaction under elevated pressure (e.g., phosphines). PA1 R.sub.1 -R.sub.5 may be bridged by suitable bifunctional substituents, such as, e.g., --(CH.sub.2).sub.x --, or --(CH.sub.2).sub.x --Z--(CH.sub.2).sub.y -- (where Z represents a hetero atom such as O, N, S; x=0-7 and y=0-7), or by unsaturated substituents (such as, straight-chain or branched C.sub.2-6 alkenyl groups and straight-chain or branched C.sub.2-6 alkynyl groups) or anellated ring systems; whereby the corresponding phenols or thiophenols are reacted with dialkyl carbonates or arylalkyl carbonates; characterized in that the process is carried out at a temperature of 70.degree.-300.degree. C. under elevated or normal pressure, in the presence of a monocyclic, bicyclic, polycyclic, or acyclic amidine as a catalyst.
The alkylation of phenols and thiophenols is commonly carried out with alkyl esters of inorganic acids or with halocarboxylic acid esters, as disclosed in Houben-Weyl, "Methoden der organischen Chemie". The methods of manufacturing phenylalkyl ethers described in Eur. Pat. 0,000,162 are particularly advantageous, however. According to this publication, phenols are reacted with dimethyl carbonate in the presence of tertiary amines or tertiary phosphines. Eur. Pat. 0,104,598 also describes an alkylation method with dimethyl carbonate, wherewith sterically hindered alkylphenols can be alkylated in the presence of a tertiary amine such as 4-dimethylaminopyridine. Another methylation with dimethyl carbonate employing tertiary amines as catalysts is described in Eur. Pat. 0,315,334, wherewith the methylation substrate is a sugar derivative, dianhydrosorbitol.
In Fr. Pat. 2,595,959, the manufacture of alkylphenyl methyl ethers by reacting alkylphenols with dimethyl carbonate in the presence of substituted guanidines is described.
Lissel, M., et al., Synthesis, 382 (1986), reacted thiophenol with dimethyl carbonate in the presence of K.sub.2 CO.sub.3 and crown ether, to obtain the corresponding thioether in about 80% yield.
The disadvantages of all of these methods are that the reactions are carried out with catalysts which:
A particular disadvantage of the ether formation catalyzed with guanidines is that these nitrogen bases tend to transfer substituents from the catalyst to the phenol which is undergoing alkylation--the result being the formation of undesirable by-products and a decrease in the effectiveness of the catalytically active guanidine system. This imposes major limitations, both as to the lifetime of the catalyst and in the choice of a suitable guanidine which will not lead to undesired side-reactions.